Borehole seismic surveys have become among the most versatile of downhole measurements used in the hydrocarbon industry. Originally, borehole seismic surveys were limited to correlating time-based surface seismic images with depth-based well logs and depth-based reservoir models for the purpose of making drilling decisions. Today, however, modern borehole seismic applications extend beyond simple time-depth correlations to generate a wide variety of useful information about reservoir extent, geometry and heterogeneity, as well as fluid content and pore-pressure, rock mechanical properties, enhanced oil-recovery progress, elastic anisotropy parameters, induced fractures geometry and natural fracture orientation and intensity. More recently, borehole seismic measurements have extended beyond applications in the hydrocarbon industry to now include applications in the hydrology and subterranean carbon sequestration industries.
Regardless of the application, deployment of seismic survey tools in boreholes has been constrained by cost and physical size considerations. For instance, in the hydrocarbon production industry, borehole seismic survey tools typically have a diameter of two or more inches and, thus, may not be deployed in a borehole if either a drillstring or tubing is in place (unless detectors are placed on the drillstring before drilling is commenced). As a result, the performance of a borehole seismic survey generally entails pulling the drillstring or production tubing (if one or the other is in place), running in an array of survey tools, conducting the survey, pulling the tool array, and then replacing the drillstring or tubing (if needed). As a result, the seismic survey is costly, both in terms of rig time and, in some instances, lost production while the survey is being performed. In addition, borehole survey tools typically include both downhole sensors and electronics. The harsh downhole environment increases the complexity and cost of the sensors and electronics since they must be designed to withstand elevated temperatures and pressures for extended periods of time. Consequently, seismic survey tools generally are not considered disposable and may not be either abandoned in the borehole after use or left inactive in a borehole for extended periods (such as for time-lapse surveys) due to lost revenues that could be obtained by deploying the survey tools in other locations.